Our lab has analyzed the phenotype, location and functional properties of lymphocytes stimulated to produce antibodies and cytokines when challenged with vaccines and conventional protein-based antigens. This work includes studies examining the immunogenicity of the envelope glycoprotein of HIV induced by natural infection, in animal models of HIV infection, and following administration of purified recombinant gp160/120. Also studied was the effect of adjuvants on the activation of cytokine producing cells, and whether early changes in the cytokine milieu effect subsequent immune responses. In these experiments, cells were obtained from mice and humans infected with the HIV or MAIDS virus, or following immunization with purified recombinant HIV envelope glycoproteins (or other protein antigens). The phenotype of the cells activated by each immunogen, and the magnitude, specificity and in vivo localization of the reactive cells, was examined. This work I) established the cytokine profile of cells located in distinct lymphoid organs, ii) enabled us to monitor the effect of selected adjuvants on the cytokines elicited by protein antigens, and iii) showed that immunizing young animals had long-term effects on the Th profile of their resting T cell pool. An antigen-specific restimulation assay was developed, permitting us to demonstrate that cytokine secreting cells activated by in vivo immunization reacted in a specific manner when re-exposed to the same antigen in vitro. In patients with HIV, changes in the frequency of type 1 and type 2 cytokine secreting cells was studied. We found that disease severity correlated with a loss of both type 1 and type 2 cytokine secreting cells, while long-term non-progressors manifest stable cytokine profiles. We showed that the relative ratio (rather than absolute number) of type 1 : type 2 cytokine secreting cells correlated best with disease progression. This ratio also appeared to influence the relative frequency of IgG1 : IgG2a secreting cells. In HIV-infected patients, monocytes were found to be major source of IL-6, IL-10 and TNFa, while T cells were the primary source of Th1 cytokines. Declining CD4 cell count correlated with a preferential loss of such Th1 secreting cells. We also examined two murine models of HIV infection. We found that MCMV infection interfered with ability of the murine AIDS virus to co-infect susceptible mice, such that the MCMV prevented the lethal sequelae of murine AIDs. In Tg mice expressing gp120 proteins from HIV, the effect of immunization on tolerance induction and disease progression was investigated.